Invasive Species: Guilty Until Proven Innocent?

A famous person once observed that the signature of a civilized mind is the ability to hold two seemingly contradictory ideas in one’s head at the same time. This is exactly what conservation must learn to do when it comes to introduced (or what we often call “non-native” or “invasive”) species.

  1. Conservation orthodoxy has it that non-native species are evil or at least highly undesirable, and that we conservationists need to do everything we can to eliminate, prevent and control any and all non-native plants and animals. Up until a few years ago, The Nature Conservancy had an entire global team specifically addressing the problem of invasive species. Today, the Conservancy’s policy team seeks regulations and trade agreements that will reduce the flow of exotic species to new lands and waters.
  2. Pointing in the opposite direction, an essay appearing this week in the journal Nature — and co-authored by several of the world’s premier ecologists — argues that we should assess organisms on their environmental impact rather than on whether or not they are native. (Did you know that the common pheasant — image above — was an introduced species to North America from Asia in 1857?)

These two views are not as contradictory as the media will portray them — but no one has recently accused the media of having a civilized mind.

Start holding these ideas together in your head:

1.     Non-native species can have devastating impacts, especially on islands. Exotic pests (such as the emerald ash borer) and plant pathogens cause enormous economic damage. Some plant invaders totally remake ecosystems — altering fire regime, nutrient cycling, productivity and resident animals. Some introduced animals have devastated fish, bird and lizard diversity.

2.     But non-native plants can also provide habitat for endangered species, and when landscapes have been trashed, exotic trees with rapid growth can be the best bet for erosion and mudslide control.

3.     Trade restrictions and border inspections substantially (and relatively cost-effectively) reduce the flood of non-native pests, and some eradication programs have succeeded. For example, on Santa Cruz Island (off the coast of southern California), the Conservancy has eliminated pigs and in the process greatly enhanced the prospects for the highly endangered island fox.

4.     But millions of dollars have been spent by federal agencies to control certain invasive species that have no measurable impacts on biodiversity or ecosystem function, and that in the end are not even reduced by the investment — in other words, lots of money has been wasted.

5.     It is important to protect ecosystems from certain invaders that could radically change the communities and overwhelm native species.

6.     But we must admit that novel ecosystems are increasingly common and these may contain non-native species that will have to be treated as “part of the ecosystem” going forward.

Some of my colleagues in conservation will label the Nature article by Mark Davis and eighteen other ecologists  “dangerous” or “destructive” because it puts forth the even-numbered ideas above. It will be interpreted as undermining existing programs to prevent or control invasive species. I do not view it that way. I see it as a provocative essay intended to make us think about how we invest our limited conservation energy and funds.

Science-based conservation cannot be about knee-jerk platitudes and simple views of good and evil. Policy experts and conservationists who have been working hard to control invasive species should not discourage arguments about invasive species — the fact is we cannot control all invasive species, and in many cases, yesterday’s invaders have become plants and animals that are beloved by local people. The concept of “nativeness” did not even really appear in the literature until the mid-19th century, the construct of the British botanists John Henslow and (later) Hewitt (H.C.) Watson.

We — both in the Conservancy and in the broader conservation world — need to take seriously the challenges issued by Mark Davis and his colleagues, and think about what they mean for where we invest our money. Triage is an act of responsibility, not surrender. I am confident that The Nature Conservancy’s investment in eradicating pigs from Santa Cruz Island was smart. I am equally confident that polices restricting the flow of non-native plants into the country could reduce future economic damage from non-native insects and pathogens. But I have also seen money spent on futile invasive control programs or on targeting non-natives that are relatively inconsequential.

I once co-authored a paper about non-native species entitled “Reducing the risks of nonindigenous species introductions: Guilty until proven innocent.” Upon reading the article by Mark Davis, I would amend that title with: “Guilty, but take into account special circumstances when sentencing.”

(Image: Common or Ring-necked pheasant. Image credit: matt knoth/Flicker through a Creative Commons license.)

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  1. Great write, Peter.

    Personally, I felt a great deal of relief in reading tomorrow’s Davis et al. paper. I feel like as we move away from the “platitudes and simple views of good and evil,” more of these articles will be coming out. I have heard horror stories of fellow researchers that have found positive effects of invasive species on ecosystems (e.g., increased biodiversity).

    That being said, hopefully this will contribute greatly to what I sense is a rhetorical and philosophical pendular shift towards a better understanding of non-natives.

    Another point, albeit less tangible, is that I sometimes ponder the idea that resistance to any non-natives can be a problem, or a artifact of our (US) western roots. That is, the idea that “nature” is in a different domain than us and that there is an idealized form of what it should be and not be is based in the idea that we have dominion over the World.

    Just some thoughts, and thanks for the preemption.

  2. This concept and post is a good one. There are many “non-native” plants that we use everyday for food, spice, and more.

    The big difference is the agressiveness of the plants and their often correlating level of harm. While non-native and invasive are typically used interchangeably, I do wish they were seperately defined. A tomatoe plant is not native (from South America)but isn’t invasively spreading while Garlic Mustard is not native and invasively taking over ecosystems. It seems it isn’t the native vs. non-native part that should be of concern but whether it is invasive or not.

    Thank you for your ideas and the post.

  3. Not only is the pheasant an introduced species, it pushed the native prairie chicken from it’s territories, helping to make it endangered. Invasive is still invasive, even if it has some perceived good use – what you are not taking into consideration is the native species that will disappear with competition, usually unfair (no predators), from the non-natives.

  4. To say nothing of all the spp that have disappeared or will with the invasives invasion of what used to be the Tall Grass Prairies due to initial stripping by ag.
    True, we will never be able to control many of the invasives that have already taken over large swaths, but we better be real sure of what we stand to lose by not controlling “lesser” ones (for now)and new ones. And, the consequences of letting others continue to spread.
    However, under the new TNC mission, I suppose whatever serves the economy best is now the new “conservation” mantra!

  5. Pheasants are beautiful birds that provide a rich benefit to the environment through sportsman’s dollars, license fees and excise taxes all of which aid economies and provide funding for habitat improvements and purchases that aid game and non-game species alike.

    I know what he’s saying on the plants. We have invasive honeysuckle but the deer and birds love it, so I don’t cut many down.

  6. A harder question is: what if they ARE invasive? When is it OK to douse the countryside repeatedly, year after year, with toxic chemicals to fight invasive weeds versus accepting the invasive land cover as the new normal? Does it all come down to what cattle will eat?

  7. I think there is still confusion over the difference between non-native and invasive. Invasive species, by the federal definition, are non-native species that CAUSE HARM to the environment, economy, or human health. If they do not cause harm, they are not invasive. So no, we do not go chasing after non-native species that are simply growing in a system and not causing a measurable adverse impact. Assessing the risk of particular invasive species to a particular system and determining what effort we should make to control it is what we do on a daily basis. I think most of us working on the ground are puzzled by this discussion and would invite anyone interested out to the field to see what we actually do. I’m getting the sense that since the loss of the Invasive Species Team we have lost an important communication link to some of science, and it would be nice to reconnect.
    And please – putting the picture of ring-necked pheasant at the top of the blog is just salt in the wound. I have a similar pretty picture of it in our office invasive species display, with the explanation of the adverse impacts it has had on prairie chickens in Indiana. Unfortunate choice.

  8. I am one of several NY TNC staff [names below*] involved in invasive species work both on the ground and in policy related efforts who fully agree with Ellen Jacquart’s comments about invasive species. The two supposedly opposing views Peter outlines are not at all contradictory. Invasive species are those that cause, or are likely to cause, “economic or environmental harm or harm to human Health” (Federal Executive Order 13112, 1999). Only a small percent of non-native species are invasive species, and only these invasive species should be the focus of prevention efforts and appropriate management.

    Staff of The Nature Conservancy who work on the threat of invasive species understand this critical distinction and act accordingly. Apparently we need to better communicate the strategic focus of our work, and the importance of prevention and carefully targeted management of truly invasive species to maintaining and restoring the health of terrestrial, freshwater and marine ecosystems.
    *Chris Zimmerman; Alpa Pandya, Hilary Smith; Gregg Sargis and others.

  9. I don’t know what effect Ring-necked Pheasants have had on Prairie Chickens in Illinois, but I suspect their decline here has more to do with lack of suitable habitat. It seems that the entire state is now farmed where it isn’t urban, with little remaining habitat for wildlife of all kinds. I do, however, appreciate the distinction between invasive and non-native.

  10. The dogmatic preference for native over non-native plants is unfortunate. We rely on non-native species for food, for our gardens, for our fibers (those that aren’t petroleum-based, anyway). Naturalized non-native plants often provide habitat for native plants and animals.

    But these novel ecosystems are often targeted for destruction — because they’re non-native. These “restored” habitats then need preservation with repeated pesticide use. ‘Non-native’ or ‘alien’ and ‘invasive’ are terms with unfortunate overtones, the one racist and the other militaristic. It’s time for a pragmatic focus, specifically on those species that are actually destructive, not just ecologically successful. It’s not just a matter of scarce resources. It’s also a matter of respecting change and changed ecosystems.

  11. If the Conservancy is serious about evaluating its restoration projects in the context of this more balanced view of non-native species, it will make a distinction between natural succession and environmental degradation.

    For over 25 years, the Conservancy has participated in efforts to reverse the natural succession from prairie to shrubs and forests in the Chicago area. Natural succession to shrubs and forests occurs when Native Americans no longer burn the prairie to prevent succession and grazing megafauna have disappeared. Millions of mostly native trees have been destroyed. Toxic herbicides are used and prescribed burns are conducted in residential neighborhoods, endangering homes and polluting the air. These “management actions” must be continued in perpetuity if natural succession is to be prevented. There is nothing “natural” about these projects and there is little doubt that they are doing more harm than good in the environment.

    In addition to wasting money on efforts that are often futile, the Conservancy should take into consideration that the “management actions” in some of these projects are damaging the environment

  12. It seems to me the argument presented is really about how resources are being allocated. The ecologists writing the article feel that too many resources have been put into the control of certain invasive species. They believe these resources could be better used on other project. The other projects likely being these ecologist’s own personal projects. Wouldn’t we all like more funding? It is just a fact of life that some areas will have more money than other areas. If the counties and towns who have money want to use it to control a species deemed invasive, then that is there prerogative. Even if a non-native species would not cause a paradigm shift in an ecosystem, there are still valid arguments for controlling them. Some people would do it just for the sake of historical accuracy.

    The people who are against cutting down trees and using herbicide have entirely abdicated there role as architects of ecosystems. They would rather see irreplaceable ancient life forms go extinct than see good management and stewardship occurring. The actions of humans have allowed certain ecosystems to form. Preventing the human actions that allow these ecosystems to persist will spell their doom. This is something that does not seem to bother the anti-management people. However, the vast majority want good management on their public lands. So, it will continue.

  13. Those who object to the needless destruction of plants and animals rarely do so for economic reasons in contrast to those who are engaged in the “restoration” industry that has evolved out of invasion biology.
    Destroying plants and animals for the “sake of historical accuracy” is surely a weak argument given that the selection of any particular historical period is entirely arbitrary.
    Scientific evidence is that non-native species other than plant pathogens have rarely caused extinctions outside of islands. The extinction argument is used to justify eradications that are rarely necessary to prevent extinctions.
    While the “vast majority” probably wants “good management of public lands,” few would likely define good management as massive native plant restorations requiring destruction of healthy plants and trees, herbicide use, or prescribed burns. A Gallup Poll in 2009, put “extinction of plant and animals species” near the bottom of a list of environmental concerns respondents were “personally concerned about.” Respodents in a ABC News/Stanford University poll in 2008, put “loss of habitat/overdevelopment” at the bottom of a list of the “single biggest environmental problem the world faces at this time.”
    If the destruction continues, it is because there is a great deal of economic interest invested in it, not because it is necessary or because of public support, which is minimal.

  14. I have met many of the people who selflessly volunteer their time to control invasive species. They are some of our smartest and hardest working citizens. These people earn nothing for all their hard work. They see a problem and rollup their sleeves and get things done. When they get together there is hardly a venue large enough to hold them all. Unlike the majority of people in this country, they are involved in the community. They also have a large constituency that votes and even runs for office.

    In a landscape highly altered by human activities, historical records are often the best source of information on which species are suited for a given site.

    Difficult decisions must be made when doing management. Removing invasive species has been shown to help populations of native species recover. Many of these invasive species make public lands less valuable for recreation and less enjoyable to visit. Most people would prefer to see a scene of native wildflowers than impenetrable thickets of introduced thorny scrub.

    The Nature Conservancy would be well advised to continue to engage with communities to control invasive species on their lands. It is not only the right thing to do for conservation. It makes the conservation properties valuable assets for communities instead of appearing like neglected vacant parcels of land.

    I respect your concerns. I love trees too. I just feel it is a shame that after the invasion of non-native invasive trees, many wonderful native species are not able to grow to adulthood. In particular, I am concerned about the future of our state tree — the White Oak.

  15. We have had very different experiences with “restorations” in the San Francisco Bay Area. In the San Francisco Bay Area, there is a small, but dedicated group of volunteers, but most of the work is being done by paid employees of the owners of public lands.

    Herbicides are often applied by employees of sub-contractors. In San Francisco the contracted firm is paid $9,000 per application of herbicide. The manufacturers of these herbicides engage in advocacy for “weed management” projects and they fund the conferences of the organizations that perform the work. When volunteers apply herbicides they are doing so in violation of policies because they don’t have the required training or equipment. We see that done, but it is not done legally.

    Likewise trees are not supposed to be destroyed by volunteers who are not qualified to use chainsaws or the heavy equipment needed to chip or remove the felled tree. Most of the trees are destroyed by huge tree companies that often engage in advocacy for these “restorations.” Early in the ascendancy of the native plant movement in the Bay Area, thousands of mature non-native trees were girdled by “volunteers” as well as paid employees in our public lands. Many of these trees are still in the process of dying. Only after a huge public outcry was this vandalism finally stopped.

    Prescribed burns must also be conducted by paid professionals.

    The historical record of which period are you trying to replicate? The landscape changes over time. Is the landscape you wish to replicate appropriate to current conditions? Have the climate, the air quality, the soil changed since then? Are the plants you wish to return to this altered landscape viable in current conditions? These are the questions that are never asked and answered by the romantic vision of native plant restorations in the Bay Area. These restorations are therefore rarely successful.

    Native plant restorations in the Bay Area do not usually improve recreational access. They are often fenced. In the current edition of its newsletter, the local chapter Sierra Club announces its opposition to the Recreational and Open Space Element (ROSE) of the General Plan of the city/county of San Francisco. Here is one of their many objections to this plan: “The draft ROSE talks about the benefits of open space for physical fitness through exercise and recreation, but these one can do on city streets or gyms.” The parks of San Francisco are apparently not for the purpose of recreation in the opinion of the Sierra Club.

    Apparently the aesthetic results of our local restorations are also different from yours. The “restorations” almost without exception are weedy messes that resemble “neglected vacant parcels of land.” Your support for the native plant movement is apparently based on difference experiences. My opposition to the native plant movement is also based on my experience.

  16. As a literate person, I’m somewhat offended by the opening line of this blog post. You open as if its a mysterious quote, when actually it is a paraphrasing of an F. Scott Fitzgerald quote from his 1936 book “Cracked up”. The original quote says nothing of being “civilized” it is “a test of first rate intelligence”. As someone who is in a profession where citation is a daily part of the job, I would think you might acknowledge your source. The full quote is as follows: “Before I go on with this short history, let me make a general observation – the test of a first-rate intelligence is the ability to hold two opposed ideas in the mind at the same time, and still retain the ability to function.
    One should, for example, be able to see that things are hopeless and yet be determined to make them otherwise. “

  17. “The concept of “nativeness” did not even really appear in the literature until the mid-19th century, the construct of the British botanists John Henslow and (later) Hewitt (H.C.) Watson.”

    And? Just out of curiousity, could you give any citations in the invasive biology field (not historians of science) of papers that actually quote Henslow or Watson on native species?

    Henslow was a great influence for Darwin, but for invasion biology?

  18. If more people knew how to use the invasive species for the food or medicine value the plants would be gathered enough to curb the invasion and the people would be healthier in the process, Every green herb is a positive statement out of Genesis 1 and indicates people should be eating these, Less study more faith.

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